Piston for an internal combustion engine

ABSTRACT

A cooling structure for an internal combustion engine piston is provided. The piston includes an oil cooling channel integrated in the piston. The oil cooling channel has a bottom surface facing towards a top surface of the piston and a top surface facing away from the top surface of the piston. The oil cooling channel is provided with an oil inlet and an oil outlet which are laterally separated from each other. The bottom surface and/or the top surface of the oil cooling channel is slanted relative to a central axis of a wrist pin opening provided in said piston.

The present application is a continuation of U.S. application Ser. No.13/002/339, filed Jan. 3, 2011, which is the U.S. National Stage ofPCT/SE2008/000426, filed Jul. 3, 2008.

BACKGROUND AND SUMMARY

The present invention relates to a cooling structure for an internalcombustion engine piston.

Cooled pistons having an oil inlet are known from example U.S. Pat. No.3,221,718 and DE 3733964. The oil inlets used as catch funnels forcooling oil that is dispensed from an oil spraying nozzle connected withthe engine housing have inners walls that are configured to be funnelshaped, cylindrical, oval or in the form of a venture jet. In order toachieve better distribution, in the cooling duct, of the oil captured inthis manner, additional dividers are inserted into the wall of thecooling duct, which lie opposite the exit surface of the oil inlet.

Using such shaping structures, the result supposed to be achieved isthat the oil stream that widens from the oil spraying nozzle is capturedand passed to the cooling duct. These structures demonstrates defects inachieving a continuous oil fill level of the cooling duct, due todisadvantageous flow and friction conditions during entry of the coolingoil into the inlet.

U.S. Pat. No. 7,051,684 tries to overcome the above mentioned problemsand shortcomings. However, in U.S. Pat. No. 7,051,684 there is still aproblem with the fill level in the oil cooling duct and the amount ofoil circulating in said oil cooling duct in said piston for achievesufficient cooling of the piston. Especially, there is a problem if theoil level in the oil duct in said piston becomes to small. The small oillevel may cause too much air to be mixed with the oil when the enginerev is in a higher range. Air is a very bad thermal conductor, whichdecreases the cooling efficiency dramatically. Another problem with thedesign of U.S. Pat. No. 7,051,684 is that the circulation of oil in theoil cooling duct is to low. A too low circulation of oil in the oilcooling duct will further decrease the cooling efficiency.

It is desirable to provide a cooling structure for an internalcombustion piston which is more efficient compared to the conventionalstructures.

According to a first aspect of the invention it is provided a coolingstructure for an internal combustion engine piston comprising an oilcooling channel integrated in said piston. Said oil cooling channelhaving a bottom surface facing towards a top surface of said piston anda top surface facing away from said top surface of the piston, said oilcooling channel is provided with an oil inlet and an oil outlet whichare laterally separated from each other. Said bottom surface and/or saidtop surface of said oil cooling channel is slanted relative to a centralaxis of wrist pin opening provided in said piston.

An advantage of this aspect is that the oil flow can be bettercontrolled resulting in improved cooling efficiency.

Another advantage is that oil may be forced from the oil inlet to theoil outlet in almost a complete rotation of a crank axle in saidinternal combustion engine.

In another example embodiment of the present invention said bottomsurface is slanted downwards, relative to said wrist pin opening, fromthe oil inlet to the oil outlet.

An advantage of this embodiment is that oil is forced to the outletautomatically while the piston is moved from a Bottom Dead Centre (BDC)to a Top Dead Centre (TDC).

In another example embodiment of the present invention said top surfaceis slanted upwards, relative to said wrist pin opening, from the oilinlet to the oil outlet.

An advantage of this embodiment is that oil is forced to the outletautomatically while the piston is moved from the TDC to the BDC.

In still another example embodiment of the present invention said oiloutlet is provided with a mechanical stop.

An advantage of this embodiment is that the oil level can be bettercontrolled.

In yet another example embodiment of the present invention said oilinlet is provided with a mechanical stop.

An advantage of this embodiment is that the oil circulation can bebetter controlled.

In another aspect of the present invention it is provided a method ofcooling a piston in an internal combustion engine, comprising the stepsof: providing an oil cooling channel in said piston, providing oil intosaid oil cooling channel via an oil inlet, transferring oil from saidoil inlet to an oil outlet provided in said oil channel, forcing saidoil from said oil inlet to said oil outlet by a bottom surface of saidoil cooling channel which is slanted relative to a central axis of awrist pin opening provided in said piston while said piston is movingfrom a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC) and/or by atop surface of said oil cooling channel which is slanted in an oppositedirection relative said bottom surface while said piston is moving fromthe TDC to the BDC.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above mentioned and otherobjects and advantages may best be understood from the followingdetailed description of the embodiments, but not restricted to theembodiments, wherein is shown schematically:

FIG. 1 is a schematic cross sectional view of an example embodiment of acooling structure for an internal combustion engine piston according tothe present invention,

DETAILED DESCRIPTION

FIG. 1 depicts schematically a cross sectional view of an exampleembodiment according to the present invention of a cooling structure foran internal combustion engine piston 100. Said piston 100 comprising abody 101, a top surface 112, a combustion chamber cavity 114, an oilcooling channel 102, a wrist pin opening 104, an oil inlet 121, an oilinlet mechanical stop 120, an oil outlet 131, and an oil outletmechanical stop 130.

Oil is provided to the oil cooling channel 102 in said piston by anozzle 145 attached to an oil pump 140. The oil is injected into the oilinlet 121 in the piston from below as indicated by arrows 147 in FIG. 1.The oil pump 140 may be the same pump as used to circulate oil to theengine bearings. A separate pump 140 may also be used for injecting oilto the pistons.

The combustion chamber cavity is typical for self igniting engines suchas diesel engines. However, a top portion in natural aspirated gasolineengines may very well have the opposite, i.e., instead of a cavity adome for increasing the compression ratio. These two examplesillustrates that there are numerous different design of the top portionof a piston depending on which fuel is used and which purpose orperformance one wants to optimize.

The body 101 of the piston 100 may be manufactured of any material whichcan resist the temperatures in the combustion chamber, mainly aluminumalloys are used for that purpose though other alloys may be seen.

In FIG. 1, the position of the wrist pin hole 104 is located below theoil cooling channel 102. The position of the wrist pin hole may varybetween different piston designs and may be arranged close to the top ofthe piston, in the middle or closer to the bottom of the piston.

The oil cooling channel 102 is integrated in the piston 100. Said oilcooling channel 102 having a bottom surface facing towards the topsurface 112 of said piston 100 and provided with an oil inlet 121 and anoil outlet 131 which are laterally separated to each other. The bottomsurface of said oil cooling channel 102 is slanted relative to a centralaxis of a wrist pin opening 104 provided in said piston 100.

In FIG. 1 said slanted bottom surface of said oil cooling channel 102 isbetter understood from lines 180 and 182. Line 184 is a linerepresenting the central axis of the piston 100. Line 182 represents aline perpendicular to said central axis 184 of the piston 100. Line 180represents a line in parallel with the bottom surface of said oilcooling channel 102. The bottom surface is slanted downwards from theoil inlet 121 to the oil outlet 131 in FIG. 1. A slope is indicated isdenoted by 108 may be in the range of 0.1-20 degrees. When the piston ismoved from a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC) oil isforced to the bottom surface of the oil cooling channel and due to itsslope forced from the oil inlet 121 to the oil outlet 131.

A top surface of said oil cooling channel 102 may be slanted in anopposite direction compared to the bottom surface, i.e., when the pistonis moved from is moved from the TDC to the BDC oil is forced to the topsurface of the oil cooling channel and due to its slope forced from theoil inlet 121 to the oil outlet 131.

In one example embodiment there is only a slope of the bottom surface ofthe oil cooling channel 102. In another example embodiment there is onlya slope in the top surface of the oil cooling channel 102. In stillanother example embodiment there is a slope of the bottom surface aswell as the top surface of the oil cooling channel 102. The slope of thetop surface of the oil cooling channel may have a different inverseslope angle compared to the bottom surface.

The oil outlet is provided with the mechanical stop 130. This mechanicalstop 130 serves to prohibit all oil from escaping from the oil coolingchannel 102, i.e., the stop will make sure that there is always some oilin the oil cooling channel 102 for cooling the piston 100. By selectinga suitable slope of the bottom surface of the oil cooling channel onemay optimize the cooling efficiency to ones desire.

The oil inlet 121 is also provided with a mechanical stop 120. Thismechanical stop 120 has the functionality to prevent oil from escapingout of the oil inlet 121, i.e., forcing the oil to circulate from theoil inlet 121 to the oil outlet 131.

A height of the mechanical stop 130 is denoted with 110, which may beselected out of the desired performance, i.e., a higher mechanical stopwill make sure that more oil is collected within the oil cooling channelat a given moment. A height of the mechanical stop 120 is denoted with106 and a higher mechanical stop 106 may result in more oil circulatingto the outlet 131 at a given moment compared to if one is using a lowermechanical stop 120. The amount of oil injected to the oil coolingchannel 102 may be determined from a pump pressure and flow from thepump 140. This may be adjusted for different purposes, i.e., a higherpump pressure may be used if one wants more cooling efficiency and/orthe nozzle may be exchanged to one with more flow capacity.

The cooling structure may be provided in a vehicle such as a lorry,truck, bus, personal car, wheel loader, construction equipment vehiclesetc.

The invention may be applied to any internal combustion engine such asdiesel engine, gasoline engine, bifuel/flexifuel engine with one or aplurality of cylinders.

The invention must not be regarded as being limited to the examples ofembodiment described above, a number of further variants andmodifications being feasible without departing from the scope of thefollowing claims.

1. A cooling structure for an internal combustion engine pistoncomprising an oil cooling channel integrated in the piston, the oilcooling channel having a bottom surface facing towards a top surface ofthe piston and a top surface facing away from the top surface of thepiston, the oil cooling channel being provided with an oil inlet and anoil outlet which are laterally separated from each other, the bottomsurface and/or the top surface of the oil cooling channel being slantedrelative to a central axis of a wrist pin opening provided in thepiston, wherein the bottom surface is slanted downwards, relative to thewrist pin opening, from the oil inlet to the oil outlet, and the topsurface is slanted upwards, relative to the wrist pin opening, from theoil inlet to the oil outlet. 2-3. (canceled)
 4. The cooling structureaccording to claim 1, wherein the oil outlet is provided with amechanical stop.
 5. The cooling structure according to claim 1, whereinthe oil inlet is provided with a mechanical stop.
 6. A method of coolinga piston in an internal combustion engine, comprising the steps ofproviding an oil cooling channel in the piston, providing oil into theoil cooling channel via an oil inlet, transferring oil from the oilinlet to an oil outlet provided in the oil channel, forcing the oil fromthe oil inlet to the oil outlet by a bottom surface of the oil coolingchannel which is slanted relative to a central axis of a wrist pinopening provided in the piston while the piston is moving from a BottomDead Centre (BDC) to a Top Dead Centre (TDC) and/or by a top surface ofthe oil cooling channel which is slanted in an opposite directionrelative the bottom surface while the piston is moving from the TDC tothe BDC.